Desensitization of photographic emulsions



neutral emulsions.

Patented Nov. 18, 1941 UNITED STATES PATENT OFFICE 2,263.00: i A nnsnusmza'ggg gf iggomanarmc Edward a... mu, weaumne, Mamland. assignor to Eastman Kodak Rochester, N. Y., a corporation of New Jersey.

No Drawing. Application May 15, 1040, Serial Compa y.

No. 335,339. In Great Britain August 15, 1989 BOlaims.

sions can be desensitized with. for example, mercuric cyanide, plnakryptol yellow and pinakryptol green. It has now been found that 3:6-diamino 1.2.4.5.tetrazines are powerful desensitizersfor Such compounds have the general formula: I

n. /N=N\ 'R.

ya. N-N- m' where R1, Ra, Ra, Rt-file hydrogen, alhyl, such as methyl. or ethyl, aryl, such as phenyl or tolyl,

aralkyl such as phenylethyl, or acyl such as acetyl, propionyl or benzoyl, or other monovalent organic radicals. The most powerful desensitizing elect appears to be exerted by the simple diamine where R1, Ra, Re, and R4 are all hydrogen atoms. At a concentration as low as .0002 gram per litre. simple 3:6-diaminotetrazine lowers the speed of a fast negative emulsion to less than half its original speed.

According to the present invention, therefore.

- a photographic emulsion, particularly a gelatinosilver halide emulsion, is desensitized by treatment' withna substituted. or unsubstituted 3:6- diaminotetrazine. The treatment may take place by bathing the emulsion before development may be kept in the form of a stock solution of a one part in one thousand parts of water and such solutlonis also quite stable to light and air. It is a reducing agent and will develop a latent image but the salts are water-soluble solids 5 generally yellow in colour and are not reducing llents. at the concsn The red solution of the free base evention indicated does not stain the so vel per. Since thedeveloper-desensitizes roughly ous. Although it is a developer, it has no harmful eiiect on latent images as is-shown by the fact that an exposed photographic :plate bathed for two minutes in a one-inflve thousand aqueous solution shows no trace of latent image destruction. Its desensitiaing power is, like that of pinakryptol yellow, effected by sulphite in the developer but its desensitizing power is comparable with that of mercuric cyanide or pinakryptol green, disregarding the effect of the developer.

The'following table shows the desensitizing effect of the free base in three different concentrafingers or gelatine orfilm and not poisontions compared with t ee known desensitizers.

A panchromatic film- W treated for two minutes in the desensitizing'solution and exposed for two minutes through a tricolour and neutralbalanced stepwedge, 1' metre from a 25 watt lamp and then developed in the dark. In the table is shown the light intensity required to give the density of .1 above the fog.

Desensitisatlon Fog Neutral Blue In the above on the des'en'sitizing agent was neglected.

six minutes in the dark. Under these conditions the desensitizing action of the 'tetrazine was Green table the effect of the developer In thegfollowing table we show similar com- 5 greatly reduced at concentrations of l in 10,000

and 1 in 5,000. Concentrations of l in 2.000 or In the table the ratio of light intensities togive a density of 0.1 above fog is shown. Since the controlis treated without first desensitizing it shows only'the desensitizing' effect due to the del in 1,000 still had good desensitizing properties.

. curic cyanide.

to one-sixth oi the initial speed, the total desensitization is represented by the figure for the desensitization alone multiplied by six.;

where R1. Ra, R: and R4 are selected from the group consis1 ting of hydrogen, alkyl, aryl, aralkyL. and acy High fog density.

As can ,be seen the eifect oi the developer on the desensitizer for at least 4-6 minutes after bathing at 1:2,000 is negligible.

Although the desensitizing power of -3:6-diaminotetrazine is less than that of pinakryptol green, or pinakryptol yellow, it is sufliciently powerful for practical purposes and for the same fog density is practically equal to that or mer- On the other hand, mercuric cyanide brings about a latent image destruction equivalent'to reduction in speed of 50% at 112,000 and about 30% at 1:10,000', whereas 3:6-diaminotetrazine, as stated above, has no action.

The manufacture of 3:6-diaminotetrazine is given in Gazzetta ChimicaItaliana, 43 (2) (1913) at page 162 and 45 (I) at page 182.

I claim:

1. The method of desensitizing a gelatino-silver halide emulsion prepared by the neutral process. which comprises treating it in a bath containing a compound having the following formula: I

2. The method of desensitizlng a gelatino-silver halide emulsion prepared by the neutral 20 process, which comprises treating it in a bath containing a 3:6-diaminotetrazine.

3. The method of desensitizing a gelatino-silver halide emulsion prepared by the neutral process, which comprises treating it after exposure in 25 a bath containing a 3:6-diaminotetrazine.

4. The method of desensitizing a gelatino-silver halide emulsion prepared by the neutral process, which comprises treating it after exposure in a bath containing a 3:6-diaminotetrazine in an amount of at least 0.0002 gram per liter.

5. The method of desensitiaing a gelatino-silver halide emulsion prepared by the neutral process, which comprises exposing it and developing it in a, bath containing a 3:6-diaminotetrazine in 35 an amount oi at least 0.00.02 gram per liter.

EDWARD B. KNo'rr. 

